Preparation of zeolites

ABSTRACT

CRYSTALLINE ALUMINOSILICATE ZEOLITES ARE RAPIDLY AND EFFICIENTLY PREPARED BY SEEDING AN AQUEOUS MIXTURE CONTAINING ALUMINA, SILICA, AND ALKALI METAL HYDROXIDE WITH ZEOLITE SEEDS, I.E. NUCLEATION CENTERS HAVING AN AVERAGE SIZE BELOW ABOUT 0.1 MICRON.

United States Patent 3,808,326 PREPARATION OF ZEOLITES Carl V. McDaniel,Laurel, Philip K. Mather, Baltimore, and Joseph M. Pilato, SilverSpring, Md., assignors to W. R. Grace & Co., New York, N.Y.

No Drawing. Continuation of application Ser. No. 126,323, Mar. 19, 1971,which is a continuation of application Ser. No. 738,116, June 19, 1968,now abandoned. This application Dec. 4, 1972, Ser. No. 311,990

Int. Cl. C01b 33/28 US. Cl. 423-329 Claims ABSTRACT OF THE DISCLOSURECrystalline aluminosilicate zeolites are rapidly and efficientlyprepared by seeding an aqueous mixture containing alumina, silica, andalkali metal hydroxide with zeolite seeds, i.e. nucleation centershaving an average size below about 0.1 micron.

This application is a continuation of application Ser. No. 126,323,filed Mar. 19, 1971, which is a continuation of application Ser. No. 738,116, filed June 19, 1968, both now abandoned.

The present invention relates to the production of crystallinealuminosilicates, and more specifically to improved methods for rapidlyand efficiently producing crystalline zeolites from aqueous mixture ofalumina, silica and alkali metal hydroxide.

It is generally known that crystalline aluminosilicates,

frequently referred to as molecular sieves or crystalline zeolites, maybe synthetically prepared from alkaline mixtures of silica and alumina.For example, in the preparation of synthetic faujasite, i.e. Type X andtype Y molecular sieves, the prior art discloses methods which involvepreparing alkaline mixtures of required alumina and silica precursormaterial, and aging the mixture at various temperatures for a period of1 to 2 days.

While prior methods have prepared synthetic crystalline zeolites of goodquality, the extended production times required for their preparationhas made these materials relatively expensive.

,,the following detailed description and specific examples.

Broadly, our invention comprises a method for preparing crystallinealuminosilicate zeolites which involves seeding an alkaline precursormixture of alumina and silica with small size zeolite seeds having anaverage particle size below about 0.1 micron, and subsequently reactingthe mixture to obtain substantial yields of crystalline zeolite.

More specifically, we have found that the processing time required toobtain substantial yields of crystalline aluminosilicate zeolite may bedrastically reduced by add- 3,808,326 Patented Apr. 30, 1974 ice ing aslittle as from about 0.1 percent to about 10 percent by weight of anextremely finely divided zeolite seeds having particle size below about0.1 micron to a precursor mixture of alkali metal hydroxide, alumina andsilica.

While it is contemplated that from about 0.1 to 10% by weight of seedparticles will yield the most economical results under mostcircumstances, amounts in excess of 10% may be used if desired. However,amounts in excess of 10% do not substantially increase the formationrate of product. For example, it is found that by using theaforementioned minor amounts of seed particles which represent onlyabout 0.1 to 10 percent by weight of the desired final product, an agingor crystallization period of only about 10 to 30 minutes is required toobtain substantially theoretical yields of faujasite having a silica toalumina ratio of about 2 to 4. Furthermore, it is found that .by usingour present seeding technique, synthetic faujasite having a silica toalumina ratio in excess of 4 may be readily obtained using inexpensivealkali metal silicate solutions as a source of silica.

The small size zeolite seeds utilized in the present seeding techniquepossess a composition similar to that of the zeolite being produced.Typically, these small sized seed particles may be of the generalformula assigned to synthetic faujasite. Synthetic faujasite which isfrequently referred to as Type X or Type Y molecular sieve dependingupon the silica to alumina ratio thereof, may be prepared in the form ofextremely fine sized particles using techniques generally disclosed inpreviously filed U.S. applications 624,997, filed Mar. 22, 1967, and633,- 355, filed Apr. 21, 1967, both now abandoned, and incorporated byreference herein.

In one preferred embodiment of the invention the seed particles arehighly crystallinein nature and may be described as representing thefinal product of the aforereferred to applications. However, it is alsocontemplated that the seed particles may possess a relatively low degreeof crystallinity, and may be typically obtained by the techniques of theaforementioned applications where in the aging period (wherein crystalsare formed) is decreased.

The aqueous precursor mixtures of silica, alumina and alkali metalhydroxide are prepared using ratios of ingredients required to producethe desired zeolite product. In the case of synthetic faujasite, forexample, the ratio of silica to alumina will vary according to thesilica to alumina ratio desired in the final product. For typicalpreparations of Type X synthetic faujasite, that is where the finalsilica to alumina ratio will be from about 2.0 to 3.0, the followingratios or concentrations of ingredients are generally followed:

Slog/A1203 3 to 5 M O/SiO 1.2 to 1.5 H O/Na O 35 to HgO/NazO 20-60 20-6012-90 In the above formulae, wherein the alkali metal cation isindicated as M, it is to be understood that while the preferred alkalimetal is sodium, other alkali metal cations such as potassium, lithiumand so forth, may sometimes be used.

The precursor mixtures which contain water, alkali metal hydroxide,silica and alumina are prepared using conventional mixing techniques andstarting materials such as sodium silicate and sodium aluminate. Othersources of silica and alumina may include alumina gel, aluminum salts,silica gel and silica sol. In general these mixtures are maintained at atemperature of from about 25 to about 110 C. and are found to remainstable for reasonable periods.

Subsequent to preparing the precursor zeolite mixtures the mixture iscombined with from about 0.1 to 10 percent by weight of zeolite seeds.The mixing procedure used in combining the seed crystals with theprecursor mixture should be one which results in a rapid and thoroughdispersion of the seeds throughout the mixture. While it is generallycontemplated that from about 0.1 to about 10 percent by weight (based onthe weight of the final theoretical yield of zeolite product) isgenerally utilized in the present technique, it should be understoodthat in excess of 10 percent by weight seed crystals may be utilized toobtain a similar result. However, amounts of seed crystals in excess ofabout 10 percent do not increase the rate of zeolite production inproportion to the economic 'value of the additional seed material.Likewise while less than 0.1 percent by weight of seed crystals may beused, it is generally found that the rate of production decreasesrapidly when less then about 0.1 percent by weight of seed crystals isutilized.

The slurry of precursor mixture and seed crystals is subsequentlymaintained at a temperature of from about 60 to about 110 C. for aperiod generally ranging from about 10 minutes to 4 hours, howeverlonger reaction periods may be employed if desired. It is found thatduring this reaction period the desired crystalline zeolite forms inyields which approach the theoretical yield expected from the startingmaterials present in the precursor solution. The reaction period maybeconducted at a relatively uniform temperature or if desired, the periodmay be conducted at a series of different temperatures. That is, theprepared slurry may be first aged at a temperature of from 25 to 40 C.for a period of 10 minutes to 24 hours, and subsequently heated to ahigher temperature of from about 40 to about 110 C. for a period ofabout 10 minutes to 4 hours. It is also to be understood that theagingreaction period may be conducted while the temperature iscontinuously varied.

Subsequent to reaction the resultant crystallized prodnet is recoveredby any convenient technique which may involve filtration orcentrifuging. The recovered product is preferably washed to removeexcess reactants, and subsequently may be dried or used in the form ofan aqueous slurry. The crystalline zeolites prepared in accordance withthe present invention have many applications including ingredients incatalysts and as absorbents.

Having described the basic aspects of the present invention thefollowing examples are given to illustrated specific embodimentsthereof.

EFMMPLE I d Zeolite seeds were prepared by the following proceures:

(A) 29 g. of sodium aluminate (Na O.Al O .3H O) was dissolved in 368 g.H O. A sodium silicate solution comprising 420 g. of sodium silicate(28.5% SiO 8.7% Na O), 112 g. NaOH and 100 g. H O was prepared. Thesesolutions were cooled to C., mixed, and aged with stirring to 1 hour at0 C. The mixture was then aged without stirring at 20 C. for 16 hours.The mixture was heated at 90 to 100 C. for 6 hours and the product wasrecovered by filtration and washed. The

product possessed the crystalline structure of Type X zeolite and asilica to alumina ratio of about 2.5. The particle size of the productwas between 0.01 to 0.05 micron. The nitrogen surface area was 720 m./g.

(B) The procedure set forth in A above was repeated, however, theheating period at -100" C. was eliminated and the 20 C. aging period wasreduced from 16 hours to about 4 hours. The resultant zeolite seedproduct possessed a particle size of below about 0.01 micron, a silicato alumina ratio of about 2.5, and no detectable crystallinity.

EXAMPLE II In the runs tabulated below various ratios of reactants, i.e.Na O, A1 0 S102, H O using sodium hydroxide, commercial sodium silicate(Na O.3.3SiO and sodium aluminate, were combined with 0.5% by weight ofseed particles A or B prepared in Example I. The preparation procedureinvolved combining the reactants, aging for 16 hours at 20 C., and aging4 hours at about 901l0 C. The resultant zeolite particles possessed asilica to alumina ratio of about 5.0 to 6.0 and the crystallinestructure of faujasite.

TABLE I Composition of reaction mix (moles) Seeds Surface Unit (A orarea cell Com- Run Na; A1 0; S101 11 0 B) (mfl/g.) (A) ments 3. 8 1 9. 5136 A 910 24. 67 Good Y.

EXAMPLE III A series of runs were made in a manner similar to that setforth in Example II, however, the 16 hour at 20 C. aging period wasomitted. Where applicable, the concentration of zeolite seeds was again0.5% by weight of the theoretical weight of the finished zeolite product(based on A1 0 It is to be particularly noted that when the zeoliteseeds were omitted, no zeolite formation occurred. (Run 1). Thus it isseen the present process provides a method for obtaining high silicafaujasite, i.e. silica to alumina ratio of 5.0, without including anexternal cold aging step.

TABLE II Composition of reaction mix (SZeds Surface Uniltl; C

or area ce om- Bun Na; 151,0 S10; 1130 B) (ml/g.) (A) ments 1..---- 3.81 9.5 136 None 2..--.-.. 3.8 1 9.5 136 A 3 3.9 1 10.0 140 B 4 4.1 1 10.5144 A 5---... 4.2 1 11.0 148 B 6 1 11. 5 152 .A. 1 12. 0 156 B 1 12. 5160 A 1 13. 0 164 B 1 13. 5 168 A 1 14. 0 172 B 1 14. 5 176 A EXAMPLE IVA series of runs were made using a reaction ratio of Na :Al O :SiO :H Oof 4.2.:1:3:180 using a solution prepared from sodium aluminate, sodiumhydroxide and sodium silicate. Various seeding levels using seedsprepared by way of the procedures set forth as A in Example I. The agingperiods conducted both at 20 C. and reflux (90-110" C.) were alsovaried. The products obtained were identified as faujasite having asilica to alumina ratio of about 2.5.

TABLE III Seeds (percent by .wt.) 20 0.

Surface Aging -do-.-. 30 minutes-...

1 Seed added before 20 O. aging. 1 Seed added after 20 C. aging.

EXAMPLE V To further illustrate the elfect of adding 1% seeds to thepreparation of Example IV, runs were made wherein the product wassampled at various 90-110 C. aging times up to 30 minutes. No 20 C.aging period was used.

Reflux Surface area mJ/g.

time (min.) 1% seeds No seeds The above examples clearly indicate thatsubstantial yields of synthetic crystalline zeolites may be rapidly andefiiciently prepared in accordance with the invention set forth herein.

We claim:

1. A method for preparing a crystalline aluminosilicate zeolite whichcomprises:

(1) preparing an aqueous precursor mixture of silica, alumina and alkalimetal hydroxide, the proportions of said silica, alumina and alkalimetal hydroxide being those required to produce the desired zeolite;

(2) adding to said precursor mixture from about 0.1 to about 10 percentby weight based on the weight of the theoretical yield of desiredzeolite of amorphous aluminosilicate zeolitic nucleation centers havinga particle size below about 0.1 micron; and

(3) reacting the mixture at a,temperature of about to C. for a period oftime sufiicient to produce a substantially theoretical yield ofcrystalline zeolite.

2. The method of claim 1 wherein the zeolite is synthetic faujasite.

3. The method of claim 2 wherein the zeolite is type X.

4. The method of claim 2 wherein the zeolite is type Y.

5. The method of claim 2 wherein the reacting period ranges from about 5minutes to 4 hours.

6. The method of claim 2 wherein the average particle size of saidfinely divided'nucleation centers ranges from about 0.01 to about 0.1microns.

7. The method of claim 2 wherein the alkali metal hydroxide is sodiumhydroxide.

8. The method of claim 4 wherein the silica to alumina ratio of thezeolite is greater than about 4.

9. The method of claim 8 wherein the silica is derived from solublesodium silicate.

10. The method of claim 9 wherein the silica to alumina ratio of thezeolite is greater than about 4.5.

References Cited UNITED STATES PATENTS 2,882,244 4/ 1959 Milton 423-3282,979,381 4/ 1961 Gottstine et al 423-329 3,119,660 1/1964 Howell et al423-118 3,071,434 1/ 1963 Frilette et a1. 423-329 3,321,272 5/1967 Kerr423-329 3,433,589 3/1969 Ciric et al 423-329 3,516,786 6/1970 Maher etal. 423329 3,574,538 4/1971 McDaniel et a1 423329 3,639,099 2/ 1972'Elliott et al. 423-329 EDWARD J. MEROS, Primary Examiner US. Cl. X.R.4231 18 3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 3, 808, 326 Dated April 30,?1974 Inventor(s) Carl V. McDaniel,Philip K. Maher and Joseph M. Pilato It is certified that error appearsin the above-identified patent and that said Letters Patent are herebycorrected as shown below:

"In Column 1, line 3:

"Carl V. McDaniel, Laurel, Philip K. Mather, Baltimore,"

should read:

"Carl V. McDaniel, Laurel, Philip K. Maher, Baltimore,"

Signed and sealed this 10th day of September" 197 (SEAL) Attest:

C. MARSHALL DANN Commissioner of Patents MCCOY M. GIBSON, JR. AttestingOfficer

